1. Field of the Invention
The present invention relates to acrylic resin compositions, and more particularly but not by way of limitation, to an acrylic monomer based polymerization syrup having an improved shelf life which. In one aspect the present invention relates to an acrylic monomer containing polymerization syrup which, upon addition of a quaternary ammonium salt polymerization catalyst, is curable at ambient temperatures and pressure.
2. Brief Description of the Prior Art
Acrylic resins formed predominantly of methyl methacrylate have heretofore been known. Because acrylic resins formed of methyl methacrylate are linear polymers, the polymers have exhibited good weatherability and transparency. However, such polymers have suffered from disadvantages in that they are deficient in resistance to heat, solvents, shock, and surface hardness. Because of these deficiencies the prior art is replete with acrylic based resin compositions wherein the base polymer, i.e. methyl methacrylate, is copolymerized with other polymers in an effort to overcome the before-stated deficiencies of such resins. Examples of several plastic resin compositions, and methods for producing such compositions which have heretofore been employed to overcome the inherent deficiencies of the acrylic resin compositions wherein methyl methacrylate is employed as the base monomer are U S. Pat.No. 4,791,184, issued Dec. 13, 1988 to Nagai, et. al.; U.S. Pat. No. 4,319,003, issued Mar. 9, 1982 to Gardlund; U.S. Pat. No. 4,214,064, issued July 22, 1980 to Kanazawa; U.S. Pat. No. 4,152,506, issued May 1, 1979 to Novak; and U.S. Pat. No. 3,957,921, issued May 18, 1976 to Iwahashi, et. al.
While various methods and resin compositions have been proposed for improving the resistance to heat, solvents, shock and surface hardness of acrylic based resins (without sacrificing the desired properties of weatherability and transparency of such resins), the resulting modified polymers have a tendency to become colored on heating and the desired properties of weatherability, transparency and color are often sacrificed or reduced.
Thus, it would be desirable if one could develop a polymerization syrup of an acrylic monomer which would maintain all of the desired properties of an acrylic resin, while at the same time overcome the known deficiencies of an acrylic resin. Further, it would also be desirable if one could formulate an acrylic resin composition which maintains its desired properties when cast into thick sheets or articles, and which would be substantially void or bubble free, and which did not require post curing. It is to such a polymerization syrup and resin composition that the present invention is directed.